The physics of twin-fluid jet-in-crossflow at atmospheric and jet-engine operating conditions

Efforts to mitigate jet engine emissions produced a class of swirl-stabilized combustors in which a rich pilot-flame in the center of the swirl-cup anchors an outer-annulus of lean-premixed main-flame. Fuel distribution within the annulus must be carefully controlled to allow stable combustion while avoiding excessive swirl-cup heating and flashbacks. This was traditionally achieved by placing plain jet-in-crossflow (JICF) fuel injectors around the swirl-cup; however, a recent increase in engine operating pressure and temperature along with demand for leaner fuel-air mixtures made the traditional approach untenable. Hence, modern swirl-cup designs begin to adopt a new fuel-injection technique called the "twin-fluid JICF (TF-JICF)" where a sleeve of air is co-injected with the liquid jet to modify its spray-pattern. TF-JICF is a nascent variation of the JICF that is not well understood, especially at elevated pressures. Hence, an experimental investigation of TF-JICF spray behaviors was performed by our group, covering the operating conditions of 1.5-9.5 atm in crossflow pressure, 175-1050 in crossflow Weber number, 5-40 in momentum flux-ratio, and 0%-150% in air-nozzle pressure-drop, at the crossflow temperature of 150 degrees C and velocity of 75 m/s. Part 1 of the investigation's results, which identified four distinct flow regimes and nonmonotonic penetration trends in TF-JICF, vas published in the work of Tan et al., "The regimes of twin-fluid jet-in-crossflow at atmospheric and jet-engine operating conditions," Phy; Fluids 30, 025101 (2018); The current paper expands upon the previous report by elucidating key spray features and potential mechanisms (e.g., transitions between crossflow-driven atomization, air-driven shear-atomization, and air-driven prompt-atomization) within each TF-JICF regime, thereby providing a conceptual framework of TF-JICF for future studies. Published under license by AIP Publishing.